1. Field of the Invention
This invention relates to cyclotron resonance maser amplifiers and to waveguide windows in such devices and other microwave power devices, and more particularly, to windows which are capable of propagating high frequency, high power microwave energy without overheating, significant mode conversion, or excessive sensitivity to frequency.
2. Description of the Prior Art
A waveguide window in a microwave power system generally permits power to pass from one waveguide to a second waveguide, but presents a physical barrier between the two waveguides. The waveguides may contain different gases or have different pressure levels, and one or both waveguides may be evacuated. For example, in high power microwave vacuum devices, such as gyrotrons and the like, power is generally transferred between an evacuated chamber or waveguide in the device and a waveguide having a gaseous environment through one or more waveguide windows which provide a hermetic seal between the two media.
A window of the prior art may consist of a disk secured in a waveguide. At low frequencies and low power, the heat generated due to inherent dielectric loss may be dissipated by cooling the edge of the disk. However, as the frequency or power is increased, cooling becomes more difficult, because more heat is generated in the window. If the additional heat is not adequately dissipated, the window may overheat and fail.
Another known window has a pair of disks with a dielectric liquid flowing between them for cooling. At high frequency or high power, the coolant pressure and consequently the window thickness is increased significantly to dissipate the added heat generated. If the disks become several wavelengths thick, however, they become very frequency sensitive, particularly when used in microwave tubes, and sensitive to variations in the dielectric constant of the disk material. In addition, the heat transfer through the thick disks is poor.
A plurality of relatively small apertures have been used for transferring microwave power from a circular waveguide to a rectangular waveguide. Since each of the coupling apertures is small, if dielectric plugs are used to provide a seal, the plugs may be easily edge cooled, and the plurality of apertures may transfer high power in the megawatt range. However, mode conversion is likely to occur in such systems at the frequencies and powers of interest here, where many modes can propagate in the waveguide, because the power transfers through a single common wall of the two waveguides in a manner which is not symmetrical. Thus, there is a need for a waveguide window which is not excessively sensitive to frequency or material variations, may be easily cooled, and does not encourage mode conversion.
Waveguide windows have had application in cyclotron resonance maser devices, such as gyrotrons. See, for example, Flyagin, V. A., et al., "The Gyrotron," IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-25, No. 6June 1977, pp. 514-521, particularly FIG. 1, where microwave energy is extracted through an end window.